1. Field of the Invention
The present invention relates to a choke valve device in a carburetor including a carburetor body which has an intake passage and in which a valve stem of a choke valve for opening and closing the intake passage at a location upstream of the intake passage is rotatably carried, and particularly to an improvement in the choke valve device in the carburetor, which is designed so that a choke valve fully closed prior to the starting of an engine is fully opened automatically after the starting of an engine.
2. Description of the Related Art
Such a choke valve device in the carburetor is already known, as disclosed, for example, in Japanese Patent Utility Model Application Laid-open No.61-25563.
In the above-described choke valve device described in Japanese Patent Utility Model Application Laid-open No.61-25563, an operating member for opening a choke lever secured to a valve stem of a choke valve and a diaphragm device adapted to be operated by an intake negative pressure in an engine are connected to the choke lever, and when the engine is started with the choke valve fully closed by the operating member, the diaphragm device is operated by an intake negative pressure generated with the starting of the engine, and the choke valve is fully opened by an operating force of the diaphragm device.
In this conventional choke valve device, the number of parts is large and the diaphragm device is expensive, inevitably leading to an increase in cost is.
Accordingly, it is an object of the present invention to provide a choke valve device in a carburetor, wherein a choke valve can be opened automatically with a simple structure having a decreased number of parts.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a choke valve device in a carburetor including a carburetor body which has an intake passage and in which a valve stem of a choke valve for opening and closing the intake passage at a location upstream of the intake passage is rotatably carried, wherein the choke valve is biased in an opening direction by a spring. A negative pressure operating chamber is provided in the carburetor body to communicate with the intake passage at a location downstream from the choke valve; wherein a locking piston is mounted in the carburetor body with its pressure-receiving face facing the negative pressure operating chamber and is adapted to be advanced and retracted between a locked position and an unlocked position, the locking piston being biased toward the locked position by a locking spring. A choke lever secured to said valve stem is provided with a locking portion which restrains said choke lever at the fully closed position in such a manner that said locking portion engages with said locking piston advanced to said locked position by a biasing force of said locking spring, when said choke lever has been turned to a fully closed position of said choke valve. The locking piston is retracted to the unlocked position and disengaged from the locking portion when an intake negative pressure equal to or greater than a predetermined value is introduced into the negative pressure operating chamber upon starting the engine.
With the first feature, when the choke lever is moved to the fully closed position of the choke valve prior to the starting of the engine, the locking piston can be advanced to the locked position by the biasing force of the locking spring to come into engagement with the locking portion of the choke lever, thereby restraining the choke lever in the fully closed position.
The engine is started, and the intake negative pressure generated in the engine is transmitted to the intake passage and inhibited by the choke valve in the fully closed state from being released to the atmospheric air. That is, the intake negative pressure equal to or greater than the predetermined value is introduced into the negative pressure operating chamber, whereby the locking piston is pulled toward the unlocked position against the biasing force of the locking spring. Therefore, the locking piston is disengaged from the locking portion of the choke lever to release the choke lever, so that the choke lever biased by the spring in the fully opening direction is turned automatically to the fully opened position of the choke valve, thereby restoring the choke valve to the fully opened state.
Moreover, the choke valve device has a simple structure with a very small number of parts, as compared with the conventional choke valve device using the diaphragm device. Therefore, the choke valve device can be provided at a low cost.
According to a second aspect and feature of the present invention, in addition to the first feature, the choke lever has a sliding surface which slidably receives an outer end face of the locking piston and inhibits the advancing of the locking piston toward the locked position of the locking piston when the choke valve is in a position other than the fully closed position.
With the second feature, when the negative pressure introduced into the negative pressure operating chamber is decreased by opening the choke valve after the starting of the engine, the locking piston is about to be advanced again toward the locked position by the biasing force of the locking spring. However, the sliding surface of the choke lever already moved in the fully opened position of the choke valve receives the locking piston, and inhibits the advancing of the piston toward the locked position. Therefore, it is unnecessary to mount a member exclusive for preventing the slipping-off of the locking piston, so that the structure can be further simplified.
The locking portion corresponds to a locking recess 23 in an embodiment of the present invention which will be described below.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.